White’s Electronics TDI SL 7.5 and 12 - Manual (Page 12)

Page 12
TDI SL
Owner’s Manual
Ground Balance
This control is used to balance out
the signal from ground mineralization.
There is an
OFF
position for which TDI
runs in straight PI mode with no
ground balance.
To ground balance TDI the
Target
Conductivity
control must be set to
ALL
in order to hear both conductivity tones. Set the
Gain
to about the
mid-point or until the audio just begins to chatter. Pump the
search coil up and down from about one inch off the ground up to
6-8 inches above the ground while listening for a change in the
audio. If the GB is too low, the audio will have a high tone when
the coil is lowered to the ground; if the GB is too high, the audio
will have a low tone. Adjust the
Ground Balance
control for min-
imal audio changes. For most moderate mineralization, this will
be around “8”. A simple technique is to start with the GB set
intentionally too low (say, 5), then pump the coil and increase the
GB until the high tone begins to transition to a low tone.
If the
Pulse Delay
control is changed, you will probably
need to re-adjust the
Ground Balance
setting. In addition, if you
begin to hear ground noises (false signals) as you sweep the coil
you should check the ground balance.
There are some cases where a particular target will fall
exactly on top of the ground balance point and TDI will not be
able to detect it at all. Targets that are close to the ground bal-
ance point may have their response shifted if the
Ground Bal-
ance
control is adjusted. For example, a given target may have a
low conductor response with GB=9 but a high conductor
response at GB=5.
Turning the Ground Balance to the OFF position disables
the ground balance and TDI will run as a straight PI detector.
This gives a slight improvement in depth but, of course, will
respond to mineralization and eliminates the ability to discern
conductivities.